Chapter-2-continuation.pdf

Princess Rose Parinasan,RRT. Chapter 2. X-RADIATIONS, or X-RAYS are type of electromagnetic radiation. Electromagnetic radiation refers to radiation that has both electrical and magnetic properties. The Dual Nature of X-ray Energy  X-rays act both the waves and like particles Wavelength an...

Princess Rose Parinasan,RRT. Chapter 2. X-RADIATIONS, or X-RAYS are type of electromagnetic radiation. Electromagnetic radiation refers to radiation that has both electrical and magnetic properties. The Dual Nature of X-ray Energy  X-rays act both the waves and like particles Wavelength and Frequency  wavelength and frequency are inversely related. If one increases, the other decreases. PROPERTIES OF X-RAYS: 1. X-rays are invisible 2. X-rays are electrically neutral. They have neither a positive nor a negative charge, therefore they cannot be accelerated or made to change direction by magnet or electrical field. 3. X-rays have no mass. They create no resistance to being put into motion and cannot produce force. 4. X-rays travel at the speed of light in vacuum. They move at a constant velocity of 3x108 m/s or 186,000 miles/in a vacuum. 5. X-rays cannot be optically focused. Optical lenses have no ability in focusing or refracting x- ray photons 6. X-rays form a poly energetic or heterogeneous beam. The x-ray beam that is used in diagnostic radiography is composed of photons that have many different energies. The maximum energy that a photon in any beam may have is expressed by the kilovoltage peak (kVp) that is set on the control panel of the radiographic unit by the radiographer. 7. X-rays can be produced in a range of energies. There is useful for different purposes in diagnostic radiography. The medically useful diagnostic range of x-ray energies extends up to 20 to 150kvp 8. X-rays travel in straight lines. X-rays used in diagnostic radiography form a divergent beam which each individual photon travels in a straight line. 9. X-rays cause some substances to fluoresce. When X-rays strikes substances, those substances produce light. These substances are used in diagnostic radiography, in intensifying screens, and in image intensifiers used in fluoroscopy. 10. X-rays cause chemical changes to occur in radiographic and photographic film. X-rays can cause images to appear in radiographic film and can cause images to appear on radiographic film and are capable of fogging photographic film. 11. X-rays can penetrate the human body. X-rays have the ability to pass through the body, based on the energy of the x-rays and on the composition and thickness of the tissues being exposed. 12. X-rays can be absorbed or scattered by tissues in the human body. Depending on the energy of an individual x-ray photon, that photon may be absorbed in the body or be made to scatter, moving in another direction. 13. X-rays can produce secondary radiation. When x-rays are absorbed as a result of specific type of interaction with matter, the photoelectric effect, a secondary or characteristic photon, will be produced. Princess Rose Parinasan,RRT. 14. X-rays can cause chemical and biological damage to living tissues. Through excitation and ionization of atoms comprising cells, damage to those cells an occur. THE X-RAY BEAM The x-ray tube is the most important part of the x-ray machine because the tube is where the x- rays are produced. X-RAY PRODUCTION The production of x-rays requires a rapidly moving stream of electrons that are suddenly decelerated or stopped. The source of electron is the cathode, or the negative electrode. Electrons are stopped or decelerated by the anode, or the positive electrode. Electrons move between the cathode and the anode because there is difference in charge between the electrodes. CATHODE - is a negatively charge electrode. It comprises a filament and a focusing cup FILAMENT- is a coiled tungsten wire that is the source of electrons during x-ray production. FOCUSING CUP- is made of nickel and nearly surrounds the filament. It is open at one end to allow electrons to flow freely across the tube from the cathode to anode. It has negative charge, which keeps the cloud electrons emitted from the filament from spreading apart. Its purpose is to focus the stream of electron. ANODE- is a positively charged electrode. It consists of a target and, in rotating anode tubes, a stator and rotor. The TARGET- is a metal that abruptly decelerates and stops electrons in the tube current, thereby allowing the production of x-rays. It can be either stationary or rotating. Rotating anodes are manufactured to rotate at a set speed ranging from 3000 to 10,000 revolution per minute. Is the part of the anode that is struck by the focused stream of electrons coming from the cathode. The target stops the electrons and thus creates opportunity for the production of x-rays. It is made of tungsten and rhenium alloy. This layer, or track is then embedded in a base of molybdenum and graphite. Tungsten generally makes up 90% of the composition of the rotating target, with rhenium making up the other 10%. Tungsten is used in both rotating and stationary targets because it has a high atomic number of 74 for efficient x-ray production and high melting point of 3370 degree Celsius. Stator- is an electric motor that turns the rotor at very high-speed during x-ray production. Rotor- is rigidly connected to the target through the anode stem. Dissipating Heat- As heat is produced when the x-ray exposure is made, the rotating anode conducts the heat to insulating oil that surrounds the x-ray tube. Rotating Anodes- rotating anodes can withstand higher heat loads than stationary anodes because the rotation caused a greater physical area, or focal track, to be exposed to electrons. Thermionic Emission- When the tungsten filament gains enough heat (therm), the outer shell electrons (ions) of the filament atoms are boiled off, or emitted, from the filament. Tube Current- Electrons flow in only one direction in the x-ray tube cathode to anode. This flow of electrons is called the tube current and is measured in milliAmperes. (mA) Energy conversion in the X-ray Tube- As electrons strike the anode target, approximately 99% of their kinetic energy is converted to heat, whereas only 1% (approximately) of their energy is converted to x-rays. Kilovoltage and the speed of electrons- The speed of electrons travelling from the cathode to the anode increases as the kilovoltage applied across the x-ray tube increases. Princess Rose Parinasan,RRT. The speed of electrons and the quality of the x-rays- the speed of the electrons in the tube current determines the quality or energy of the x-rays produced, the quality of the energy of the x- rays that are produced determines the penetrability of the primary beam. KVP and BEAM penetrability- as kVp increases, beam penetrability increases; as Kvp decreases, beam penetrability increases. kVp and X-ray quality- higher kVp results in electrons that move faster in the tube current from cathode to anode.  The FASTER the electrons in the tube current move, the greater the quality of the x-rays produced.  The greater the quality of x-rays produces, the greater the penetrability of the primary beam. MILLIAMPERAGE, TUBE CURRENT and X-RAY QUALITY MILIAMPERE (ma)  Is the unit used to measure the tube current. Tube current measures the number of electrons flowing per unit time between the cathode and anode.  The quantity of electrons in the tube current and quality of x-rays produced are directly proportional to the milliamperage. MA and X-RAY quantity:  Higher mA results in more electrons that move in the tube current from cathode to anode  The more electrons in the tube current, the more x-rays that will be produced  The number of x-rays that are produced is directly proportional to mA. EXPOSURE TIME(s)  Determines the length of time that the x-ray tube produces x-rays. EXPOSURE TIME, TUBE CURRENT, AND X-RAY QUANTITY.  The quantity of electrons that flows from the cathode to anode and the quantity of x-rays produced are directly proportional to the the exposure time. EXPOSURE TIME AND X-RAYS QUANTITY:  The longer exposure time results in more electrons that move in the tube current from cathode to anode.  The more electrons in the tube current, the more x-rays produced.  The number of x-rays that are produced is directly proportional to the exposure time. Milliamperage and Time When milliamperage is multiplied by exposure time, the result is known as mAs which the radiographer may be able to set at the control panel. Mathematically mAs is simply expressed as follows: mA x S= mAs where s represents exposure time in fractions of a seconds (as actual fractions or in decimal form) or in seconds. MAS AND X-RAY QUANTITY:  Higher mAs results in more electrons that move in the tube current from cathode to anode Princess Rose Parinasan,RRT.  The more electrons in the tube current, the more x-rays that will be produced  The number of x-rays that are produce is directly proportionate to the mAs.